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Dispatches from the edge of the Empire

Hadrian’s Wall from close to Steel Rigg car park, April 2014.

My wife and mother are on holiday together in Jordan and sent me a progress report from the ruined Roman city of Jerash, complaining about the weather (31 degrees Celsius). In a spontaneous show of empathy with their plight in the south eastern corner of the Roman Empire, I decided to visit the north-western border to make my own observations about the weather (11 degrees, strong westerly winds and occasional squally showers).

Having written about Trentepohlia in the previous post, I was alert to any conspicuous orange patches as I walked along the central part of Hadrian’s Wall yesterday. The location for the pictures below is the famous Sycamore Gap (NY 761 677), which was used as a location in the film Robin Hood: Prince of Thieves, apparently. It was easy to spot the distinctive patches of Trentepohlia, even from 100 metres away. What was particularly intriguing was that I only saw it on the north-facing side of the wall. Fabio Rindi and Mike Guiry found no correlation with compass direction in their study (referenced in previous post), though Table 1 of their paper does seem to suggest a slight preference for north-facing walls in Galway. Presumably the north side of the wall receives less direct sunlight, so provides a slightly less harsh environment for the alga. My observations are, also, a rather dramatic validation of their comment about a preference for “old walls” – this section of Hadrian’s Wall having stood here for about 1900 years.

Sycamore Gap on Hadrian’s Wall (NY 761 677), with patches of Trentepohlia visible on the north side.